Nasa said the storm, currently brewing above the Atlantic Ocean, had weakened to Category 1 strength, but is expected to strengthen into a Category 3 hurricane by the time it makes landfall on the US mainland.

Once Florence makes landfall, it’ll be the first major Atlantic hurricane of the 2018 season to hit the mainland US.

Some experts have warned the storm could be the next Hurricane Katrina.

Weather Underground founder Dr Jeff Masters said: “I saw a presentation a few years ago that showed that Hurricane Katrina of 2005 increased markedly in size after it absorbed a small area of disturbed weather over the southeast Gulf of Mexico, acquiring more moisture and spin.

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STORM: Hurricane Florence off the US east coast in the Atlantic Ocean

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SPACE: NASA satellites are monitoring its strength and speed

“If Florence manages to absorb [the tropical area], the increased spin…may expand Florence's size considerably, leading to a larger storm surge and an increased area of wind and rainfall impacts.”

Katrina battered the city of New Orleans in August 2005, devastating the area and leaving more than a million people homeless.

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